Thermionic tube



June 13, 1944. E. c. EWING 'THERMIONIC TUBE Filed April -1, 1,941

Patented June 13, 1944 2,351,026 THERMIONIC TUBE Edwin C. Ewing, Chicago, Ill., assignor to Zenithv Radio Corporation, Chicago, Ill., a'corp'orati'on of Illinois Application April 1, 1941, Serial No. 386,377 8 Claims. (Cl. 250-275) The present invention relates to vacuum tubes and particularly to certain features of construction whereby tubes of this character are improved 'for amplification purposes, have an extremelylow noise level, and are especially free.

from microphonic noises.

It is one purpose of the invention to provide a 'tube'of this character wherein the filament is given adequate rigidity without applying hazardous tension thereto.

" It is a further purpose-ofthe invention to provide a tube of this character wherein'the filament to grid to plate spacing and arrangement are such as to output electrostatic side field and increase-electron concentration- Where the filament-grid plate'spacing is" such asto give the best amplification.

'It1is also a purpose of the present invention to provide a novel-construction whereby the tribulation for exhausting the-tube is main- --tainedopen during the sealing or pinch'opera- "'tion.

The'features'and advantages of the invention willappear more fully as the description proceeds in connection with the accompanying drawing.

' The drawing and "description are illustrative only -h'owever'and should not be consideredaslimiting the invention except insofar as itislimitedby the claims.

In the drawing: Fig; 1 is a. sectional view; several times en- 'larg'ed, taken'lengthwise through atube embody- ='ing my invention;

* Fig. 2 is a" sectional-*view-taken on 'theline Fig. 3 is a, sectional view similar to Fig. 1 but 'takenalongthe line at right angles thereto, illustrating a different form of plate construction, "theremain'ing elements of the tube being the same; Fig. 4 is a sectional view takenon the'line Fig. 515 a-perspectiveview of the plate element: shown in Fig. 3.

"Referring-now in detail to the drawing, the

has two wing portions I! and "3 which extend down outside the grids l2 and 43 parallel tothe filament I 4. These two Wing portions l1 and I8 are placed opposite the flattened wall portions of the grids l2 and I3 and the wings do not extend around-the envelope where the "endwall portions l9 and 20 of the gridsare located. I arrange the-plate wings in this position with respect to the grid or grids in order to prevent electrostatic side field at the point where the grids are close to the envelope and would necessarily have to be close to the plate. Also, the arrangement of the plate wings'as shown increases electron concentration at the areas where the grids are closest to the filament. Low amplification characteristics are thus avoidedand the-electron concentration is at the most desirable point.

In Figs. 3 to 5 the plate II is somewhat differently constructed to-the-plate l Ibut functions in the same manner. I use a metallic plate which may be wire mesh or solid. The wings l'l and I8 are positioned with respect tothe grids-l2 and I3 precisely as they are in Fig. 1. It-is easier with the plate II to supportit'with a supporting wire 2| whichpasses out through the I press of thetube and forms a lead-in wire forthe plate. The plate -I I may also be-usedtocarry a getter material 22 of any known'type.

Referring now to the grid-and filament mounting, the two grids -|2 and-l3- are composed of helical coils of wire mounted on suitableposts in a well known manner. A ceramic bead'23 made ofa suitable ceramic material-havingadequate mechanical strength is used to connect certain of the elements of a tube such as the two grids l2 and I 3. The bead iscomposed of a cold moldable, cold setting plastic material preferably of a ceramic base. -The plastic bead'23 is-of particular advantage in tubes of very small-dimensions like that shown herein. Glass heads' or others requiring heat cannot be-used successfully. The heat would seriously injure the-parts because of their size, particularly the" filament. Also, the deleterious-oxidizing of the partsthat results from using heat in securing them together is avoided by use of the-cold setting plastic ceramic-material. As shown herein,-the--grids are connected togetherby a bead -of this type r and other elements arealso joined :by suchbeads.

The long axis ofthe oval-shaped 'gricls is placed parallel with the plane-of the filament I l and midway between the wing portions I1- and I8 or IT and [8. of the plates. The gridsare supported by separate lead-in-wires-24 and-25 which are positioned by a glass bar 26. The

"noise level.

'fila'mentdoesnot place any strain thereon beable material. For example, it maybe a, metal suitably insulated. The bead 29 is however a; very simple and convenient means for supporting the guide hook.

The lateral guide hookcomprisesa stem porw a end-portionand two wing portions extending tion 3|, the base of which isf mounted'jin the bead29, and a rebent portion 32 at the free end of the stem 3|. ment I4 is passed between the stem'3! and the rebent portion 32 of the lateral guide hook. The

hook is a loose fit so that the filament can slide up and down upon heating and cooling. I have found by experience that the filament coating does not. loosen or wearat the point of contact with the'hoo'k and that the loss by heatcon- ,duction is negligible. I am aware that in the past it'has been the practice to hook the midpoint of the filament up to suspension hook under more or less tension. I Suitable tension on these delicate filamehtsis very difiicult toapply.

Moreover, tension in the filamentaids vibration.

By the use of; the lateral guide hook as illustrated in the drawingf'I am able to give the filament (rigidity in the right direction without applying hazardous tension thereto The critical spacing of the filamentiis with respect tothe adjacent wall portions of the grid that run parallel to the filament plane andare close .to ,thefilament, The

" guide hook keeps the'filament from swinging so fa's to change this critical spacing; The filament, when the assembly is first completed, will bear against one side-of the .hookwithfla light pressure. Howevergwhen the filament is excited or heatedthe side pressure tends to decreaseand f the filament takes a permanent set so that there 1 is merely a slight contact; with the hook Actual tests with manyofthetubes having this construction 9W .thfim t b quite .f e i i phonic noises. They have an extremely, low Expansion or contraction of the causepf its freedom to slide lengthwise of the hook- '1 c r I have provided a novel means whereby tokeep the tubulation for 1 exhausting the tube open "through the pinched end of the envelope. .Prior to compressing the end of the envelope. about the lead-in wires 24,25, 21 and 23 I provide a thin tubular lining as; within the "tubulation glass.

This linin'g 33may be constructedof .any suittube or merely'aicoating of thick graphite placed As' stated 1 herein- -Their actual dimensions are usuallyabout lin'ch overall length, includingfthe pinched: end portion, and the diameter. of the,

yeiope may be.

less than'% ofan inch.

The base of theU-shaped fila- 5 claim as new and desire to secure by Letters Patent is:

1. A vacuum tube comprising an envelope, a Y filament therein supported by its two ends, a grid encircling said filament and being flattened 10 in cross section whereby two opposite wall porj tlOIlS thereof are in close proximity to the filament and the wall portions at 90 degrees from the first named wall portions are relatively remotefromthe filament, and a plate comprising second named'grid wall portions.

2.- Avacuum tube comprising an envelope, a

gig plate, a grid and an emitter in said envelope,

said emitter including aloop'filamentsupported therein by its two ends; and Iallateral'f guide member loosely overlying said'filaznentiin proximity to the midpoint thereof, said filament being free to slide endwise'in said memberbu'tbeing held against lateral swinging imovement by said membein j '3. A vacuum tube comprising an :envelope, a plate, a grid and a U-shaped'filamenttin said envelope, leads supporting saidplate, gridand .the ends of the filament in the envelope,'andlailateral guide for said filament engaging it at .aproximately "the midpoint; said' guide: having :a channel in'which the filament is slidableendwise,

- the "channel damping-vibration of the filament in a direction perpendicular to theiplane of the filament. r l -4.-A vacuum itube comprising an'e'nvelop'e, a plat'ei a grid and a'U-shaped filament in said en- 40' velope'; leads supporting saidplate, gridi'a'nd the ends'of thefilament in the envelope, a bea'd'in'terposed between the filament and the envelope and "mechanically" "connecting the filament leads to cachothr, and a" lateral guide book for thefilaism'e'nt'carried by said head 'i 5.A vacuum tube comprising an envelopeya plate, "a" grid and a U-shaped filament in said envelope, leads'supporting said plate, gridand the ends of th filament in the envelope,"a"'glass bar between the envelope and the grid and filament "mechanicallyconnecting the leads, a bead interposed between the filament and the bar and mechanically connecting the filament leads'to each other, and a lateral guide for said filament engaging it at approximately the midpdint','said 'guide having a channel in which the filament is slidawe endwise, the channel damping vibration of "the filament'in a direction perpendicular to the plane of the filament, andsaid guide being supported by saiclbead.

6. A vacuum-tube comprising an envelope, a plate, a grid and a U-shap'edfilamentin said envelopaleads connectedto the opposite ends of said filament and supporting it within said envelope, said grid encircling the filament and being flattened in "cross section whereby-two opposite "walls thereof extnd'substantially parallel to the plane of the filament and-infclose proximity thereto; the portions of the grid connecting said oppositewalls being-relativelyremote from the filament, a supporting lead connected to onejof said connecting'portion's of the grid, 'said'pla'te comprising two wing portionsextending length- ;wise of the filament outsid'e of the aforesaid o po- ---7 site-Wall's or the' grid and 'sp'aced apart attheir side edges whereby to leave the connecting portions of the grid with no plate portions outside of them, said wing portions being connected to each other by means extending over the ends of the grid and filament opposite said supporting leads and remote from said ends, whereby the electron concentration is greatest at the areas where the grid is closest to the filament and electrostatic side field is prevented at said connecting portions of the grid.

7. A vacuum tube comprising an envelope, a plate, a grid and a U-shaped filament in said envelope, said grid encircling the filament and being flattened in cross section whereby two op-- posite walls thereof extend substantially parallel to the plane of the filament and in close proximity thereto, the portions of the grid connecting said opposite walls being relatively remote from the filament, said plate comprising two wing portions extending lengthwise of the filament outside of the aforesaid opposite walls of the grid and spaced apart at their side edges whereby to leave the connecting portions of the grid with no plate portions outside of them, said wing portions being connected to each other by means extending over the ends of the grid and filament and remote from said ends, whereby the electron con- 8. A vacuum tube comprising an envelope, a plate, a grid and a U-shaped filament in said envelope, said grid encircling the filament and being flattened in cross section whereby two opposite walls thereof extend substantially parallel to the plane of the filament and in close proximity thereto, the portions of the grid connecting said opposite walls being relatively remote from the filament, said plate comprising two wing portions extending lengthwise of the filament outside of the aforesaid opposite walls of the grid and spaced apart at their side edges whereby to leave the connecting portions of the grid with no plate portions outside of them, said wing portions being connected to each other by a getter carrying disc extending over the ends of the grid and filament and remote from said ends,

whereby the electron concentration is greatest at the areas where the grid is closest to the filament and electrostatic side field is prevented at said connecting portions of the grid.

EDWIN C. EWING. 

